Recently, research on ultra-small-sized large-capacity semiconductor memories has been actively progressing. According to such research, technologies for increasing storage capacity of semiconductor memory elements through a multichip package, in which multiple semiconductor chips are mounted in one semiconductor package, are being developed.
In order to electrically connect circuit patterns formed in such multiple semiconductor chips, via holes (TSV: through silicon via) vertically passing through a silicon wafer substrate are formed. Such via holes should be formed according to a predetermined standard. Otherwise, a malfunction of a semiconductor package may be caused. Therefore, it is necessary to inspect whether the depth and shape of such via holes have been formed normally.
A conventional scheme employs an FSI, WSI, or confocal scheme that requires using a coaxial light in order to measure the depth of a hole. However, in the case of the confocal scheme, a point where a light spatially converges by a lens is used and thus, there is a problem in that, when a narrow and long hole is measured, the light converging toward a focal point is blocked by the opening.
Further, the conventional scheme uses a single camera for the measurement. However, in the case of such a single camera scheme, it is difficult to measure/inspect an inclined surface because a small amount of light is reflected. In addition, in the case of using multiple cameras to observe a side surface of a hole, not only is it difficult to bring the cameras into focus at the same time but also a distortion may occur in an image. This is because the measurement target (which is not a flat wafer and requires simultaneous measurement of multiple holes instead of a single hole) is not perpendicular but is inclined with respect to the viewing angles of the cameras. Accordingly, a close site may be distorted to be larger while a distant site may be distorted to be smaller, and since image formation surfaces may be inclined, it is difficult to bring the cameras into focus over the entire FOV at the same time.
(Prior Art Document) Korean Patent No. 10-1407482, (Article) Applicability of diffraction grating to parallax image array generation in integral imaging: Jang-Il Ser, Jae-Young Jang, Sungdo Cha, and Seung-Ho Shin, Department of Physics, Kangwon National University, Chuncheon 200-701, South Korea.